1. Field of the Invention
The present invention relates to ball valves, and more particularly, to a valve seat assembly and a device for retracting the valve seats when it is required to disassemble and assemble a top entry ball valve.
2. Description of the Prior Art
The valve seats, in a ball valve, are annular and are sealed against the valve housing by means of an O-ring. They also include a seal which must be constantly urged against the surface of the spherical ball valve or plug because of wear to which the seals are subjected. Springs or other resilient devices may be used to urge the seal against the plug. The seals and plug must be replaced or repaired frequently because of wear which is sometimes accelerated because of abrasive substances present in the fluid.
In order to remove the plug and valve seats for inspection, the spring loaded seals must be retracted from contact with the plug to allow the plug to be rotated to a position to be lifted out of the valve housing.
There have been many attempts to provide floating or spring loaded valve seats with devices for retracting the seals in a top entry ball valve to allow the plug to be removed or inserted. U.S. Pat. No. 4,388,945, issued June 21, 1983 to Johnson et al, discusses some of the earlier attempts to provide devices for retracting the valve seals. The Johnson et al patent offers a solution in the provision of four pins with cam surfaces which are inserted into the cavity through openings provided in the housing and adapted to engage the valve seats and press them rearwardly away from the plug. Other prior art mentioned in the Johnson et al patent are U.S. Pat. No. 4,266,566, issued May 12, 1981 to Kacal et al, which includes threaded bolts for engaging the springs by frictional contact once the valve seats have been retracted by a camming device on the ball or plug. The threaded bolts screw through the valve housing into the spring opening. U.S. Pat. Nos. 3,171,431, issued Mar. 2, 1965 to Hansen et al, and 3,037,738, issued June 5, 1962 to Jackson et al, utilize a screw for advancing the seat towards the plug. However, there is no means for retracting the valve seats once the forward force has been removed.
U.S. Pat. No. 3,985,334, issued Oct. 12, 1976 to Domyan, includes an eccentric extending through the housing to engage the valve seats for retracting the valve seat against the springs.
U.S. Pat. Nos. 3,037,738, to Jackson et al; 3,171,429, issued Mar. 2, 1965 to Sturmer et al; and 4,718,444, issued Jan. 12, 1988 to Boelte; all use some form of threaded pin with a cam surface for engaging the valve seat and pushing it away from its contact with the plug. The threaded pins pass through the housing.
U.S. Pat. No. 3,269,691, issued Aug. 30, 1966, Meima et al, uses a cam pin fixed inside the housing which engages a cam follower track within the valve seat. The valve seat is rotated with a special spanner wrench inserted through the valve casing cover to rotate the valve seat, thereby causing its retraction by means of the cam pin.
All of the prior art requires relatively complicated mechanisms all of which use in one form or another pins or other devices which pass through the housing, thereby increasing the potential for leakage of the valve housing. In the prior art which does not require exterior inserted pin devices, complicated or specialized tooling must be utilized in order to accomplish the retraction of the valve seats.